The invention relates to a pump for fluids, whereby under a fluid both a gas and a liquid is to be understood.
For the displacement of sensitive liquids like especially blood, pumps have been developed in which a rotor is held in an equilibrium position within a support tube by mechanical field forces. Thus a blood pump is known from U.S. Pat. No. 5,695,471 which is configured as a radial pump with a radial rotor. The radial rotor is disposed within a support tube and has, in an inlet side projection, a plurality of rotor magnets which are juxtaposed with stator magnets on the support tube. Additionally, the radial rotor has distributed about its periphery a plurality of rod-shaped rotor magnets extending in axial direction and which are juxtaposed with ring-shaped stator magnets displaced on both sides of the radial rotor along the sides of the support tube. These rotor and stator magnets should support the radial journaling in the region of the projection of the rotor. The rotor is held purely mechanically in the axial direction at one end by a ball and at its opposite end on a point bearing.
The rotor is driven by means of a brushless rotary field or three phase motor. For this purpose, on sides of the support tube a coil is provided which cooperates with a spoked pole magnet set into the radial rotor. The drawback with this blood pump is that the journaling stability in the radial direction is not optimal and the pump, because of the multiplicity of rotor and stator magnets, requires considerable space and has a high weight. In addition, the purely mechanical bearing in the axial direction suffers from wear which is especially a disadvantage for implanted blood pumps.
Axial pumps are also known for use as blood pumps. In this case, the journaling is effected exclusively mechanically in guide wheels which are arranged at fixed locations in the support tube ahead of and behind the rotor. (Wernicke et al., A Fluid Dynamic Analysis Using Flow Visualization of the Baylor/NASA Implantable Axial Flow Blood Pump for Design Improvement, Artificial Organs 19(2), 1995, Pages 161-177). Such mechanical bearings are wear intensive and have in addition an unsatisfactory influence on sensitive liquids, especially body liquids like blood. Rotor devices with mechanically journaled rotors have been developed as well for measuring devices. Thus in German patent document 29 19 236 a turbine wheel counter is described for measurement of the flow of liquids, in which the rotor has two spaced-apart rotor magnets for radial stability which are configured as permanent magnets and are juxtaposed pairwise with stator magnets surrounding the support tube and also formed as permanent magnets. Thus the rotor and stator magnets are magnetized to repel each other in axial direction.
Between the stator magnets, an electric magnet coil is arranged which annularly surrounds the support tube. The magnet coil cooperates with a ferromagnetic flux conductive piece on the rotor which is arranged between the rotor magnets. In addition, a sensor is provided which detects the axial position of the rotor and cooperates with a control device which regulates the electric current in the magnetic coil. As soon as the field forces of the rotor and stator magnets determine that an axial shift of the rotor has occurred, the rotor is accelerated from the equilibrium position in the axial direction and the rotor, by measurement of the axial shift of the rotor, generates a signal which is effective to produce a counteracting, stabilizing field force in the magnetic coil. The rotor thus responds to an axial position shift in one or another of the devices to continuously return the rotor in one or the other direction upon an axial position shift. Thus the stabilizing axial force is so phaseshifted with respect to an axial position change that the rotor is both restored in position and is also shifted into its setpoint position by damping forces.
A drawback of the aforedescribed rotor device resides in that the rotor has only a relatively small bearing stiffness in the radial direction. The origin thereof is the distance between the stator and rotor magnets because of the annular channel provided between the carrier tube and the rotor and along which the fluid is displaced.
In German patent document DE-A-24 44 099, a magnetic bearing for rapidly moving bodies is known. This magnetic bearing has a rotor whose ends are provided with pole positions lying opposite one another and having permanent magnets and which apply attractive forces to the rotor to hold it in a stable position. By means of a contactless position sensing, deviations can be determined from the equilibrium position. Such devices are compensated by a powerless electromagnetic stray field control for which annular coils are provided which are arranged at the pole pieces proximal to the gaps with the rotor. Such a magnetic bearing is not suitable in a support tube through which a fluid is guided on spatial grounds.
The invention has as its object to provide a pump of the aforedescribed type which has significantly higher bearing stiffness, especially in the radial direction and which permits highly versatile use thereof.
These objects are attained in accordance with the invention by the following features:
a) the pump has a support tube;
b) in the support tube a rotor is rotatably journaled;
c) the rotor has displacement elements for conveying the fluid through the support tube;
d) the rotor has at both ends axially magnetized permanently magnetic rotor magnets;
e) the ends of the rotor are juxtaposed with axially-opposite permanently magnetic stator magnets connected with the support tube;
f) each stator magnet has such axial magnetization that the neighboring stator and rotor magnets opposite one another attract each other;
g) the pump has a magnetic axial stabilizing unit for the rotor; and
h) the pump has an electric motor with a stator generating a rotary field on the support tube and a spoked pole magnet on the rotor.
The object is also attained by a pump with the following features:
a) the pump has a support tube;
b) a rotor is rotatably journaled in the support tube;
c) a rotor has displacement elements for conveying the fluid through the support tube;
d) on the ends of the rotor there are each an axially-magnetized permanently magnetic magnet and a flux guide piece opposite one another, whereby the magnets are either on the rotor as rotor magnets or are connected with the support tube (2) as stator magnets;
e) the pump has a magnetic axial stabilizer unit; and
f) the pump has an electric motor with a rotary field generating stator on the support tube and a spoked pole magnet on the rotor.
The basic concept of the invention is thus, by means of rotor and stator magnets in an end orientation, to generate a magnetic field bridging the gap between rotor and stator magnets in the axial direction so that the respective opposing pairs of rotor magnets and stator magnets oppositely attract one another. As a result, the bearing stiffness with the same geometry of the magnetic bearing of DE-A-29 19 236 is increased by at least the power of ten, without affecting significantly the annular channel between the support tube and the rotor hub.
The aforedescribed effect also arises when two magnets, i.e. rotor and stator magnets, are not juxtaposed with one another but rather at each end a magnet on one side and the flux guide piece on the other side are used. Thus the magnets can alternatively be used as rotor magnets which are affixed to the rotor and the flux-conducting pieces connected to the support tube or the flux-conductive pieces can be arranged on the rotor and the magnets can be seated on the support tube as stator magnets. For producing a high bearing stiffness, additional electric magnetic coils can be provided for reinforcing the magnetization of the flux-conducting pieces in the sense of increasing the attractive force between the magnet and the flux-conducting pieces.
To the extent pairwise rotor and stator magnets are juxtaposed with one another they preferably are comprised of at least two interfitting partial magnets whereby the respective radial neighboring partial magnets are oppositely magnetized. With this configuration of the rotor and stator magnets, the bearing stiffness can be increased by around a factor of 40.
The rotor is advantageously configured as an axial rotor so that it can serve as an axial pump. Such an axial rotor is substantially less expensive to produce than a radial rotor.
According to the invention, the rotor has a rotor hub and the rotor magnets or flux-guide pieces are arranged in the rotor hub, whereby the stator magnets or the flux guide pieces are disposed opposite the ends of the rotor hub. The stator magnets or flux guide pieces can be connected to the support tube with webs or ribs which are conducive to flow. Because of this arrangement, a compact construction is provided and detrimental cracks are avoided to the greatest possible extent. The stator magnets or flux guide pieces should be arranged in radial stabilizers whose contours do not project beyond the rotor hub, whereby the radial stabilizers preferably have the same contours as the rotor hub.
In a further feature of the invention it is provided that the respective opposite ends of the radial stabilizer and the rotor are so configured that at least one is of spherical shape. Because of this feature, a mechanical engagement of regions remote from the axis of the rotor and the radial stabilizer are avoided upon axial deflection of the rotor. For limiting the radial and/or axial mobility of the rotor it is advantageous that the respective end faces of the radial stabilizer and the rotor be formed with interfitting complementary bearing pins and bearing recesses, whereby a corresponding radial play is ensured in that the bearing pin and recess only come into contact with relatively large deflections of the rotor in the radial direction. In a further feature, the invention provides that the rotor magnets and the stator magnets are arranged directly opposite one another, respectively, and thereby produce the strongest possible magnetic field.
According to the invention the axial stabilizing device have at least one electric magnet coil as well as a control unit with a sensor for the axial movement of the rotor, whereby the control unit influences the electric current flow in the magnet coil or the magnet coils so that the magnetic field of the magnetic coil or coils counters an axial movement of the rotor from its setpoint position. Such an axial stabilizing device is known in principle from DE-A-29 19 236 and DE-A-24 44 099 and has been found to be effective. There are two possibilities for the arrangement of the magnet coils, namely, one in which the coils are on the support tube in such manner that they surround the support tube, and the other in which they are located in the radial stabilizers themselves whereby precautions must be taken for leading out the conductors to and from the magnet coils. Preferably the radial stabilizers have flux-conducting pieces in such configuration and disposition that the axial magnetic field generated by the rotor and stator magnets are superimposed in the gap between the ends of the radial stabilizers and rotor by the magnetic field generated by the magnetic coil in the axial direction and, indeed, in such manner that an axial movement of the rotor out of its intended position is counteracted. The magnetic coils themselves can be used as sensors. The flux-conducting pieces are preferably disposed at the level of the magnetic coils.
To the extent that a speed determination is desired, it is advantageous to provide the rotor with a pulse generator and support tube with a pulse pickup so that the pulse generator produces pulses for the pulse pickup corresponding to the speed of the rotor. This can be achieved simply by configuring the pulse generator magnetic as magnetic pulse source and the pulse pickup as a coil. In the coil, upon rotation of the rotor, an electric current is induced.
In a further aspect of the invention it is provided that the electric motor have at the level of the rotor a rotary field stator excitable with polyphase three-phase-alternating current and to provide the rotor so that it has a radially-magnetized spoked pole magnet. The result is a synchronous motor which, upon excitation of the rotary field stator with three phase current, produces a rotating field which entrains the rotor so that rotary movement is imposed upon the rotor. The rotary unit has, therefore, motor characteristics and can be used not only for measurement purposes but also as a pump for the displacement of fluids depending upon the rotor configuration. Preferably the spoked pole magnet has at least four magnetic segments magnetized in different radial directions. This construction counteracts wobbling movement of the rotating rotor which can arise because of magnetic field asymmetry in regions of the bearing gap between rotor and radial stabilizer. The rotary field stator should be connected with an electronic three-phase generator permitting load angle regulation. The targeted regulation of the load angle both with respect to magnitude and direction allows adjustment of the rotary field or the torque and stabilization of the rotor.
The rotor is matched to the respective use. Thus the rotor can have displacement elements in the form of wing-like projections. It can however also be provided with at least one helical rib so that, between the individual turns of the rib, channels are provided which effect the displacement. Pumps of this type can be used for generating high vacuums.
Alternatively, a blade crown can be formed on the rotor hub and can overlap with a complementary scoop-shaped blade crown on the inner wall of the support tube. Depending upon the configurations of the respective blade crowns, the pump can have various use possibilities, for example, as a gas turbine or high-vacuum pump. The aforedescribed blade crown configuration can also be combined with helically oriented channels. In this manner a so-called compound pump for use in vacuum technology and with an especially high compression ratio can be made.